My understanding of Biennial plants is a plant that has a 2 year cycle, sow one year to flower the next.
Hardy describes a more robust plant that may make it through harsher conditions, such as cold weather.
So Hardy biennials may do as well in the north as they do say in the south. But this H B description is only a guide when buying/growing plants as local conditions may vary which will also affect the outcome.

It means that the plant will take 2 years to complete its growth cycle. In the first year it will mainly grow roots and leaves. In the second year , after dieing back in winter, it regrows, normally more vigorously and produces flowers and seeds. Many seed themselves around the garden so you seem to have them every year ( as if they were perennials ) e.g hollyhocks.

...... and foxgloves ....